An inflator for providing inflation fluid to inflate an inflatable device, such as an air bag, typically includes a container containing a stored pressurized gas. A rupturable closure member is fixed to the container to block flow of inflation fluid through an outlet passage. An initiator located next to the closure member, when actuated, causes the closure member to rupture so that inflation fluid can flow from the inflator. Also, a projectile or other piercing device may be used for opening the closure member.